This invention relates to a charging circuit for charging a rechargeable battery, and to a battery pack containing the charging circuit.
FIG. 3 shows a battery pack containing a prior art charging circuit disclosed in Japanese Non-examined Patent Publication HEI 7-29554 issued on Jan. 31 ,1995. In this figure, 31A and 31B are a pair of charge-discharge terminals which are connected to a charging power supply or to a discharge load. 32 is a rechargeable battery connected between the charge-discharge terminal pair 31A and 31B. Q31 is a charge control switch, which is a MOSFET (metal oxide semiconductor field effect transistor) connected in series with the rechargeable battery 32 between the charge-discharge terminal pair 31A and 31B. 33 is a charging control circuit which measures the state of charge of the rechargeable battery 32 and controls the operation of the charge control switch Q31. 34 is a detection switch which detects a connection of the battery pack and the charging power supply. The detection terminal of the detection switch 34 is exposed from the battery pack.
When a charging power supply is connected to the battery pack with this configuration, connection is detected by the detection switch 34 and power is supplied from the charging power supply to the charging control circuit 33. As a result, the charging control circuit 33 begins operation, and functions to control charging and puts the rechargeable battery 32 in an optimum state of charge.
This circuit prevents wasted consumption of the rechargeable battery power by the charging control circuit 33 when the battery pack is removed from the charging power supply. However, in addition to the charge-discharge terminals 31A and 31B, indispensable for the rechargeable battery 32 charging, a detection terminal, not inherently necessary simply for rechargeable battery 32 charging, is required to control the operation of the detection switch 34.
It is an object of the present invention to provide a charging circuit and a battery pack containing that charging circuit which has a simple configuration and which can reliably control charging while limiting wasted power consumption by the charging control circuit.